package envSensor

import (
	"encoding/hex"
	"github.com/valyala/bytebufferpool"
)

func (x DataPack) GetEnvGatherCommand() *bytebufferpool.ByteBuffer {
	buf := bytebufferpool.Get()
	x.Function = 0x03
	decodeAddress, _ := hex.DecodeString(x.Address)
	buf.Write(decodeAddress)
	buf.WriteByte(x.Function)
	buf.Write(x.Start)
	buf.Write(x.DataLen)
	x.Crc = calculateCRC16Modbus(buf.Bytes())
	buf.Write([]byte{byte(x.Crc & 0xFF), byte(x.Crc >> 8)})
	return buf
}

func calculateCRC16Modbus(data []byte) uint16 {
	var crc uint16 = 0xFFFF // CRC-16 初始化值
	for _, byteVal := range data {
		crc ^= uint16(byteVal) // 对字节进行异或操作
		for i := 0; i < 8; i++ {
			if crc&0x0001 != 0 {
				crc >>= 1
				crc ^= 0xA001 // 多项式 0xA001
			} else {
				crc >>= 1
			}
		}
	}
	return crc
}